WooCommerce: my markup changes in "archive-product.php" are overriden

Below is the default archive-product.php with only one change: I added <div id='main_content'> right after the get_header() call, and I closed this div element right before the sidebar call ( do_action( 'woocommerce_sidebar' ); ).

<?php
if ( ! defined( 'ABSPATH' ) ) exit;
get_header( 'shop' );
?>
<div id='main_content'>
<?php
    do_action( 'woocommerce_before_main_content' );
    do_action( 'woocommerce_archive_description' );
    if ( have_posts() ) :
        do_action( 'woocommerce_before_shop_loop' );
        woocommerce_product_loop_start();
        woocommerce_product_subcategories();
        while ( have_posts() ) : the_post();
            wc_get_template_part( 'content', 'product' );
        endwhile;
        woocommerce_product_loop_end();
        do_action( 'woocommerce_after_shop_loop' );
    elseif ( ! woocommerce_product_subcategories( array( 'before' => woocommerce_product_loop_start( false ), 'after' => woocommerce_product_loop_end( false ) ) ) ) :
        wc_get_template( 'loop/no-products-found.php' );
    endif;
    do_action( 'woocommerce_after_main_content' );
?>
</div>
<?php
do_action( 'woocommerce_sidebar' );
get_footer( 'shop' );
?>

Resulting markup should be:

<div id="main_content">
    <div class="row"> [WC content] </div>
</div>
<div id="sidebar"> [WC Sidebar] </div>

Instead I get:

<div id="main_content">
    <div class="row"> [WC content] </div>
    <div id="sidebar"> [WC Sidebar] </div>
</div>

That is, the sidebar seems to have magically moved to inside my new div element. Why?